1. Field of the Invention
This invention relates to an aqueous solution of atelocollagen and the method of preparing the same.
The aqueous atelocollagen solution of this invention can be injected into living bodies without any trouble; it is sufficiently fluid to allow easy injection, for example, through a fine syringe needle and is capable of regenerating collagen fiber when it becomes equilibrated with biological conditions.
2. Description of the Prior Art
Collagen is the major protein which constitutes the connective tissues of animals, such as the skin, blood vessels, cornea, tendons, bones and teeth, having a molecular weight of approximately 300,000. It has a rod-like molecular structure of helical configuration consisting of three polypeptide chains, about 3,000 .ANG. in length and about 15 .ANG. in diameter.
Collagen molecules, which are biochemically synthesized by collagen-producing cells in living bodies, are incorporated in the surrounding collageous fiber tissue and gradually change into insoluble collagen through intermolecular crosslinking.
This insoluble collagen cannot be extracted by dilute aqueous acid solutions. The juvenile collagen immediately after formation, on the other hand, can be extracted by dilute aqueous acid solutions because of the absence of crosslinks, even when it is present on or in the surrounding collagen fiber tissue. This acid-extractable collagen is called soluble collagen.
The insoluble collagen, if treated with a proteolytic enzyme, such as pepsin, undergoes fission at the intermolecular crosslinks and becomes soluble in dilute acids. During this treatment with pepsin, the telopeptide groups at both terminals of each collagen molecule are digested, thus leaving collagen with no telopeptide terminal ends. The collagen thus released is called atelocollagen. Since the telopeptide moiety is primarily responsible for antigenicity of collagen, atelocollagen has little antigenicity if any, which makes it very suitable for use as a medical material.
Use of purified collagen as a medical material for therapeutical applications has been expanding and becoming diversified. For example, purified collagen is employed as local hemostatics in the form of powder or sponge, as a traumatic cover and artificial eardrum in the form of a membrane or nonwoven fabric, and as contact lenses in a shaped form. It is also used in a molded form containing a medicine for slow release preparations. In these applications collagen is used in solid form. However, there are other fields in which use of collagen in a fluid solution state is desired. For example, there has been a demand for an aqueous solution of collagen that can be injected into ruptured tissues, for example, through a syringe needle to fill up the affected area without incision. In this case it is necessary that the collagen solution remain fluid during injection without forming fibrous structure, and that the collagen molecules contained in it become oriented into fiber form when exposed to, and equilibrated with, biological conditions after injection to produce bundles of collagen fiber. If such an aqueous solution of collagen be developed, the bundles of collagen fiber formed in living bodies will accept entry of cells and minute blood vessels from the surrounding tissue, and will maintain its volume for a sufficient period of time, thus aiding in filling up the injured part.
Use of soluble collagen or atelecollagen is indispensable to the preparation of a collagen solution having such properties. Collagen of these types is soluble in a dilute acid solution with a pH value of 5 or lower, but such an acidic solution cannot be applied to living bodies. For a collagen solution to be applicable to living bodies, preferably it has properties close to biological conditions, namely, a pH value of about 7 and an osmolality of about 280.about.290 mOsm/KgH.sub.2 O, and is preferably capable of being injected, for example, through a fine syringe needle. The acidic collagen solution mentioned above, however, tends to produce collagen fiber before injection under the conditions close to those in living bodies described above, and cannot be applied, for example, through a fine syringe needle.